Zombie
Zombies are the most common hostile mobs. They spawn in dark or dimly lit areas, and will attack the player by slowly moving toward them and inflicting damage by making contact. Like Skeletons, Zombies catch fire in sunlight. Zombies can be heard making roaring, moaning and growling noises when near. Also zombies are damaged by health potions. In addition to generic Zombies, which closely resemble an "undead" version of the Player, several rarer Zombie forms may spawn. Zombies have green skin, empty eye sockets, and identical clothing to the player and other humans. They are 2 blocks tall, 1 block wide, and 0.24 blocks thick. Zombie Villagers have the same bodies as original Zombies, but their heads appear as undead Villager heads. Baby Zombies or Baby Zombie Villagers are smaller than normal zombies. They can go through 1-block gaps, move much faster and are not harmed by sunlight. Despite their small size, both their health and their hitbox are the same as for full-sized zombies. Any of the above can also spawn wearing armor of any type, and/or wielding an iron sword or shovel. (These zombies also drop extra experience.) Whether or not they already have such possessions, a small fraction of zombies can pick up dropped items and wear/wield them. The chance for either buff depends on game and/or regional difficulty. Behavior Zombies spawn in groups of 1-6 and will pursue the player on sight. Zombies will attempt to avoid obstacles, including sheer cliffs and lava, and will try to find the shortest path towards the player. (video demonstrating the Zombie's path finding) Unlike Skeletons, Zombies do not try to avoid being hit, and continue to pursue the player even when being attacked. Zombies can sometimes deal damage through a closed door, as shown on the picture to the right. Like most mobs, Zombies will always float on water, even if their target is below them. At dawn, generally when the sun is 15 degrees or more above the ground (that is, when the moon can no longer be seen), most Zombies will catch fire and burn once exposed to direct sunlight. However, zombies with head armor are immune to sunlight, but the armor piece will take damage. They may make some attempt to seek out shade during this time, or enter bodies of water to protect themselves from burning up. Being in water, rain, or shade negates the effects of direct sunlight, preventing them from burning. Zombies will exit protective areas to chase a close player or Villager, whereupon they will again be vulnerable to burning. Zombies wearing headgear will also be protected from burning, and Baby Zombies do not burn. If they attack a player or mob while burning, they will set their victim on fire. Attacking Villagers Zombies will attack Villagers within 16 blocks. Once a Zombie has focused on a Villager, the Zombie will ignore any other Villagers, and the player, until its target is dead or the player attacks. Zombies will bang on closed wooden doors, and can succeed in breaking them down in Hard difficulty. In other difficulties, the door will crack, but not break. Iron Doors are always safe. In Minecraft Pocket Edition, zombies cannot break down wooden doors at all. In the newest updates, not all zombies will break down doors. Only zombies with a special tag can do this; since the chance of this happening is ridiculously low, only rarely will one see a zombie attack a door. If a zombie is attacking a villager and is hurt by another mob, the zombie will then retaliate and attack the offending mob. Reinforcements On Hard difficulty, Zombies can call other Zombies in the area to "help", and in a matter of seconds, more Zombies will target the player. When a zombie is damaged by another entity it will attempt to spawn one reinforcement zombie nearby (within an 80x80x80 box centered on the attacked zombie). Both the damaged zombie and the new zombie will have a reduced chance of summoning another reinforcement, so they cannot cause an infinite number of zombies to spawn, but they can multiply significantly. Damaged zombies will also call all other nearby zombies in the area to attack, regardless of difficulty, not unlike zombie pigmen. These effects can be combatted by killing the zombie in as few hits as possible, by using environmental damage such as falls or lava, or by ignoring them. Console Edition In Console Edition, most of the zombie and villager reactions are present, with zombie sieges occasionally happening. Zombies are also able to convert villagers to their zombie form. However, the special breaking down door tag is not present and as such all zombies can punch doors. Tips A lone zombie can easily become a large group, as it can spawn more zombies. Furthermore, they hit a lot harder when injured. Killing the zombie rapidly (iron or diamond sword), or leading with environmental damage, can help cut the multiplication. Blocking the zombies off with fences works fairly well, but be wary that reinforcement zombies can appear and approach from all directions. On the other hand, the multiplication makes it easy to "farm" zombies for experience, Rotten Flesh, and drops. Stone swords and moats are helpful here. Alternatively, if located in the middle of a large, well-lit area with a good view, reinforcements will be coming from a distance, making it easy to prepare and position for their arrival. A player on sufficiently high ground can repeatedly hit a Zombie as it approaches, knocking it away consistently before it gets close enough to cause damage. Being one block lower than the Zombie makes it easier to prevent contact. Like Zombie Pigmen and skeletons, Zombies have a chance of spawning equipped with armor wielding an iron sword or iron shovel, any of which may also be enchanted. Zombies, along with Zombie Pigmen, Skeletons and the Wither, are considered "undead". Thus, they can be damaged by Splash Potions of Healing, are healed by Splash Potions of Harming, and are unaffected by poison or regeneration. They likewise take extra damage from any weapon enchanted with Smite. Finally, zombies, like other undead (except the wither), catch fire in sunlight. While this will eventually kill them, it also makes them more dangerous: On top of increasing attack damage as their health drops, a burning zombie can set the player (or other victim) aflame with an attack. Zombies are vulnerable to all the usual environmental damage: lava/fire, falling, and contact with cacti. They can drown or suffocate when trapped within water or solid blocks respectively. Zombies can be prevented from calling for reinforcements by putting two trap doors behind a door. Zombies recognize an open trap door as a solid block, and will walk right into the hole. It will need two traps doors next to each other, opened, as baby zombies can run over the 1x1 hole using the edge of the first trap door. Many useful traps can be made using this method. Surface Zombie populations can be controlled if the player regularly sleeps in a bed at dusk, since Zombies will only spawn at night if the player is awake. However, they can still wander out of caves, as well as spawn in shadowy bits of surface.